First, double check that there are no additional spaces before or after the promo code (this can sometimes happen when you're copying and pasting). Then ensure that the code is not past its expiration date. If you are receiving special pricing through a special group, not all promos may be valid for you.
Additionally, we encourage you to read the terms and conditions of the promo code, if available, to ensure you are eligible (for example, many promo codes can only be redeemed once, are for first-time customers, cannot be combined with other offers, etc.)
If you are still having trouble, please contact us at firstname.lastname@example.org.